PROJECT SUMMARY/ABSTRACT ? PROJECT 4 Age-related declines in speech recognition lead to the loss of economic opportunity, social isolation, and depression. These declines are pronounced when listeners must work to recognize speech in noise, particularly older adults with metabolic presbyacusis. Project 4 examines the ability of older adults with metabolic, sensory, and neural presbyacusis to leverage acoustic-level phonetic cues that help identify speech sounds, as well as an adaptive control system that helps to optimize performance during challenging tasks. Aim 4.1 tests the hypothesis that perception of acoustic-level phonetic cues is differentially affected across metabolic, sensory, and neural presbyacusis phenotypes because of differences in the ability to represent critical low-frequency information (e.g., pitch) and brief information with rapid onsets (e.g., voice onset time). Aim 4.2 tests the hypothesis that limited function of a frontal adaptive control system results in unexpectedly poor suprathreshold speech recognition, particularly in older adults with metabolic presbyacusis, because of small vessel disease, a common cause explanation for inner ear and frontal cortical declines. Structural and functional neuroimaging data will be integrated with perceptual decision-making modeling to test these hypotheses and an overarching causal model that declines in auditory and frontal adaptive control systems affect the accumulation of spectral and temporal information and modify decision boundaries during speech recognition. The results from Project 4 are expected to explain why older adults with different mechanisms of presbyacusis experience speech recognition difficulties, which may guide counseling and the design and selection of interventions to enhance communication and quality of life.